Non-volatile memories are desirable for integrated circuits due to their ability to maintain data absent a power supply. Phase change materials have been investigated for use in non-volatile memory cells. Phase change memory cells include phase change materials, such as chalcogenide alloys, which are capable of stably transitioning at least partially between amorphous and crystalline phases. Each phase exhibits a particular resistance state and the resistance states distinguish at least two logic values of the memory cell. Specifically, an amorphous state exhibits a relatively high resistance, and a crystalline state exhibits a relatively low resistance.
As shown in FIG. 1, a typical phase change memory cell 10 has a layer 3 of phase change material between a first electrode 1, which is disposed within an insulating layer 5, and second electrode 2. As an example, the phase change material is a chalcogenide alloy, such as Ge2Sb2Te5 or SbTeAg.
A portion of the phase change material 3, the programmable volume 4, is set to a particular resistance state according to the amount of current applied via the electrodes 1, 2 and the duration of that application. To obtain an amorphous state, a relatively high write current pulse (a reset pulse) is applied through the phase change cell 10 to melt a portion of the material for a short period of time. The current is removed and the cell 10 cools rapidly to a temperature below the crystallization temperature, which results in the portion 4 of the material 3 covering bottom electrode having an amorphous phase exhibiting a high resistance. To obtain a crystalline state, a lower current write pulse (a set pulse) is applied to the phase change cell 10 for a longer period of time to heat the material to a temperature above its crystallization point and below its melting point. This causes the amorphous portion of the material to recrystallize to a crystalline phase that is maintained once the current is removed and the cell 10 is rapidly cooled.
A sought after characteristic of non-volatile memory is low power consumption. Often, however, phase change memory cells 10 require large operating currents. It is therefore desirable to provide a phase change memory cell with reduced current requirements.
One approach to reducing power consumption has been to modify the material of the phase change memory cell to achieve maximum power transfer. For example, in a GeSbTe-based phase change memory cell, one approach is to dope the entire GeSbTe-material with nitrogen, increasing its resistance. As described in more detail herein, applicant, however, has found that this approach has disadvantages.
A phase change memory cell having reduced power consumption and methods for forming the same would be desirable.